This invention relates to acoustic fluid-gauging systems and methods.
The invention is more particularly, but not exclusively concerned with ultrasonic fuel gauging systems for aircraft.
Fuel quantity in an aircraft fuel tank can be measured by means of ultrasonic probes. These consist of an ultrasonic transducer mounted at the lower end of a tube or stillwell. The probe is immersed in any fuel present so that fuel fills the stillwell to the same height as in the tank. A voltage applied to the transducer generates a burst of ultrasonic energy, which is transmitted upwardly through the fuel. When the signal meets the fuel surface, that is, its interface with the air above the fuel, a part of the energy is reflected back to the transducer. Energy received by the transducer produces a voltage; this is supplied to a suitable processor to measure the time between transmission and reception. The height of fuel above the transducer can then be calculated from the known speed of the ultrasonic pulse in the fuel. The volume of fuel in the tank is calculated from the outputs of several probes and with knowledge of the shape of the tank.
There are various problems with ultrasonic gauging systems. In particular, it can be difficult to distinguish between the signal produced by the true reflection off the fuel surface and noise signals, such as reflections from the surface of the probe. This problem can be made worse if the fuel surface is at an angle, if it is disturbed by waves or foam, is rapidly moving or is otherwise perturbed.